SiC semiconductor device having a high mobility and a high threshold voltage, inverter circuit, and vehicle

ABSTRACT

A semiconductor device including a p-type SiC layer, a gate electrode, and a gate insulating layer therebetween, the gate insulating layer including a first layer, a second layer provided between the first layer and the gate electrode and having a higher oxygen density than the first layer, a first and second regions provided in the second layer, the first region including a first element (at least one of Ta, Nb and V) having a first concentration peak, and the second region including a second element (at least one of Ge, B, Al, Ga, In, Be, Mg, Ca, Sr, Ba , La, and lanthanoid) having a second concentration peak of the second element and a third concentration peak of C, a distance between the second concentration peak and the third concentration peak being shorter than a distance between the first concentration peak and the third concentration peak.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of and claims the benefit of priorityunder 35 U.S.C. § 120 from U.S. Ser. No. 15/055,848 filed Feb. 29, 2016,and claims the benefit of priority under 35 U.S.C. § 119 from JapanesePatent Application No. 2015-061802 filed Mar. 24, 2015 and JapanesePatent Application No. 2015-236877 filed on Dec. 3, 2015, the entirecontents of each of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor device,an inverter circuit, and a vehicle.

BACKGROUND

SiC (silicon carbide) is expected as a material for a next-generationsemiconductor device. SiC have excellent physical properties. Incomparison with Si (silicon), a band gap is three times, breakdownelectric field strength is approximately ten times, and thermalconductivity is approximately three times. A low-loss semiconductordevice which can operate at a high temperature can be realized by usingsuch properties.

However, for example, an interface state density between a semiconductorand an insulating layer is increased in the case where a metal insulatorsemiconductor field effect transistor (MISFET) is formed by using SiC incomparison with the case where Si is used. Therefore, there is a problemthat mobility of electrical charges is decreased, and on-resistance ofthe MISFET is increased.

For example, there is a method in which N (nitrogen) or P (phosphorus)are introduced into the interface between SiC and an insulating layer toterminate an interface state. When this method is used, N (nitrogen) orP (phosphorus) functions as an n-type dopant, and a threshold voltage ofan n-channel type MISFET may be decreased.

In order not to cause malfunction of a SiC-MOSFET, a threshold voltageat least equal to or greater than 3 V may be required at an operationtemperature (for example, 200° C.), and preferably the threshold voltageis equal to or greater than 5 V. In case termination by nitrogen orphosphorus being applied, the threshold voltage may falls down to around1 V.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a semiconductor device accordingto a first embodiment;

FIG. 2 illustrates a crystal structure of a SiC semiconductor accordingto the first embodiment;

FIG. 3A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to the first embodiment, and FIG.3B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode;

FIG. 4 is an explanatory diagram of functions and effects according tothe first embodiment;

FIG. 5 is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to a second embodiment;

FIG. 6 is an explanatory diagram of functions and effects according tothe second embodiment;

FIG. 7A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to a third embodiment, and FIG. 7Billustrates element distribution of the SiC layer, the gate insulatinglayer, and the gate electrode;

FIG. 8 is an explanatory diagram of functions and effects according tothe third embodiment;

FIG. 9A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to a fourth embodiment, and FIG.9B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode;

FIG. 10 is an explanatory diagram of functions and effects according tothe fourth embodiment;

FIG. 11A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to a fifth embodiment, and FIG.11B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode;

FIG. 12 is an explanatory diagram of functions and effects according tothe fifth embodiment;

FIG. 13A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to a sixth embodiment, and FIG.13B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode;

FIG. 14 is an explanatory diagram of functions and effects according tothe sixth embodiment;

FIG. 15A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to a seventh embodiment, and FIG.15B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode;

FIG. 16 is an explanatory diagram of functions and effects according tothe seventh embodiment;

FIG. 17 is a schematic view of a driving device according to an eighthembodiment;

FIG. 18 is a schematic view of a vehicle according to a ninthembodiment;

FIG. 19 is a schematic view of a vehicle according to a tenthembodiment; and

FIG. 20 is a schematic view of an elevator according to an eleventhembodiment.

DETAILED DESCRIPTION

A semiconductor device according to embodiments described hereinincludes a p-type SiC layer; a gate electrode; and a gate insulatinglayer provided between the SiC layer and the gate electrode. The gateinsulating layer including; a first layer, a second layer providedbetween the first layer and the gate electrode, the second layer havinga higher oxygen density than the first layer, a first region providedacross the first layer and the second layer, the first region includinga first element which is at least one element in the group of F(fluorine), D (deuterium), and H (hydrogen) and the first region havinga first concentration peak of the first element, and a second regionprovided in the first layer, the second region including a secondelement which is at least one element in the group of Ge (germanium), B(boron), Al (aluminum), Ga (gallium), In (indium), Be (beryllium), Mg(magnesium), Ca (calcium), Sr (strontium), Ba (barium), Sc (scandium), Y(yttrium), La (lantern), and lanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, and Lu) and the second region having a secondconcentration peak of the second element and a third concentration peakof C (carbon), a distance between the second concentration peak and thethird concentration peak being shorter than a distance between the firstconcentration peak and the third concentration peak.

Embodiments of the present disclosure will be described below withreference to drawings. In description below, same or similar memberswill be denoted by same reference characters, and the description ofmembers described once will be appropriately omitted.

Further, in description below, symbols of n⁺, n, n⁻ and p⁺, p, p⁻indicate relative height of an impurity concentration in each conductiontype. Specifically, n⁺ indicates that an impurity concentration of an ntype is relatively high in comparison with n, and n⁻ indicates that theimpurity concentration of an n type is relatively low in comparison withn. Furthermore, p+ indicates that an impurity concentration of a p typeis relatively high in comparison with p, and p⁻ indicates that theimpurity concentration of a p type is relatively low in comparison withp. An n⁺ type and an n⁻ type may be simply written as an n type, and ap⁺ type and a p⁻ type may be simply written as a p type.

First Embodiment

A semiconductor device according to a first embodiment includes a p-typeSiC layer, a gate electrode, and a gate insulating layer providedbetween the SiC layer, and the gate electrode. The gate insulating layerincludes a first layer, a second layer, a first region, and a secondregion. The second layer is provided between the first layer and thegate electrode and has a higher oxygen density than the first layer. Thefirst region is provided across the first layer and the second layer.The first region includes a first element which is at least one elementin the group consisting of F (fluorine), D (deuterium), and H (hydrogen)and has a first concentration peak of the first element. The secondregion is provided in the first layer. The second region includes asecond element which is at least one element in the group consisting ofGe (germanium), B (boron), Al (aluminum), Ga (gallium), In (indium), Be(beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium),Sc (scandium), Y (yttrium), La (lantern), and lanthanoid (Ce, Pr, Nd,Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) and has a secondconcentration peak of the second element and a third concentration peakof C (carbon) in which a distance from the second concentration peak isshorter than a distance from the first concentration peak.

FIG. 1 is a schematic sectional view illustrating a configuration of aMISFET which is a semiconductor device according to the presentembodiment. A MISFET 100 is a double implantation MOSFET (DIMOSFET) inwhich a p-well and a source region are formed by ion implantation.Further, the MISFET100 is an n-channel type MOSFET in which an electronis a carrier.

The MISFET 100 includes an n⁺-type SiC substrate 12. In the presentdescription, with respect to faces of the SiC substrate 12, a face on anupper side in FIG. 1 is called a front face, and a face on a lower sideis called a back face.

The SiC substrate 12 is, for example, a SiC substrate of 4H—SiC, forexample, including N (nitrogen), in which an impurity concentration is1×10¹⁸ cm⁻³ or more and 1×10²⁰ cm⁻³ or less, as n-type impurity.

FIG. 2 illustrates a crystal structure of a SiC semiconductor. Arepresentative crystal structure of the SiC semiconductor is a hexagonalcrystal system such as 4H—SiC. One side of faces (a top face of ahexagonal prism), in which a c-axis along an axial direction of thehexagonal prism is a normal line, is a (0001) face. A face equivalent tothe (0001) face is called a silicon face and denoted as a {0001} face.Si (silicon) is arranged on the silicon face.

The other side of faces (a top face of a hexagonal prism), in which ac-axis along an axial direction of the hexagonal prism is a normal line,is a (000-1) face. A face equivalent to the (000-1) face is called acarbon face and denoted as a {000-1} face. C (carbon) is arranged on thecarbon face.

On the other hand, a side surface (prism surface) of a hexagonal prismis an m-face equivalent to a (1-100) face, in other words, a {1-100}face. Further, a face passing through a pair of ridgelines which are notneighboring is an a-face equivalent to a (11-20) face, in other words, a{11-20} face. Both of Si (silicon) and C (carbon) are arranged on them-face and the a-face.

Hereinafter, an example will be described in which a front face of theSiC substrate 12 is a face inclined at 0° or more and 8° or less withrespect to a silicon face, and a back face is a face inclined at 0° ormore and 8° or less with respect to a carbon face.

On the front face of the SiC substrate 12, for example, an n⁻ type driftlayer 14 is formed in which an impurity concentration of n-type impurityis 5×10¹⁵ cm⁻³ or more and 2×10¹⁶ cm⁻³ or less. The drift layer 14 is,for example, an epitaxial layer of SiC formed by epitaxial growing onthe SiC substrate 12.

A front face of the drift layer 14 is a face inclined at 0° or more and8° or less with respect to a silicon face. A film thickness of the driftlayer 14 is, for example, 5 μm or more and 100 μm or less.

On a part of the front face of the drift layer 14, for example, a p-typep-well region (SiC layer) 16 is formed in which an impurityconcentration of p-type impurity is 5×10¹⁵ cm⁻³ or more and 1×10¹⁷ cm⁻³or less. A depth of the p-well region 16 is, for example, around 0.6 μm.The p-well region 16 functions as a channel region of the MISFET 100.

On a part of the front face of the p-well region 16, for example, ann⁺-type source region 18 is formed in which an impurity concentration ofn-type impurity is 1×10¹⁸ cm⁻³ or more and 1×10²² cm⁻³ or less. A depthof the source region 18 is shallower than a depth of the p-well region16 and is, for example, around 0.3 μm.

Further, on a part of the front face of the p-well region 16 and on aside of the source region 18, for example, a p-well contact region 20 isformed in which an impurity concentration of p-type impurity is 1×10¹⁸cm⁻³ or more and 1×10²² cm⁻³ or less. A depth of the p-well contactregion 20 is shallower than a depth of the p-well region 16 and is, forexample, around 0.3 μm.

A gate insulating layer 128 is provided continuously on the drift layer14 and the p-well region (SiC layer) 16. The gate insulating layer isformed so as to extend over the drift layer 14 and the p-well region 16.

A gate electrode 30 is formed on the gate insulating layer 128. Forexample, doped polysilicon can be used for the gate electrode 30. On thegate electrode 30, for example, an interlayer insulating film 32 formedof a silicone oxide film is formed.

The p-well region 16 sandwiched between the source region 18 and thedrift layer 14 under the gate electrode 30 functions as a channel regionof the MISFET 100.

The gate insulating layer 128 is provided between the gate electrode 30and the p-well region (SiC layer) 16. A film thickness of the gateinsulating layer 128 is, for example, 30 nm or more and 300 nm or less.A film thickness of a silicone oxide film of the gate insulating layer128 is, for example, 30 nm or more and 60 nm or less.

FIG. 3A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to the present embodiment, andFIG. 3B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode. FIG. 3A is an enlarged view ofa p-type SiC layer 16, a gate insulating layer 128, and a gate electrode30, and FIG. 3B illustrates element distribution thereof.

The gate insulating layer 128 includes a first layer 128 a, a secondlayer 128 b, a first region 129 a, and a second region 129 b. The secondlayer 128 b is provided between the first layer 128 a and the gateelectrode 30. The second layer 128 b is provided on the first layer 128a.

The first layer 128 a and the second layer 128 b are, for example, anoxide film or an oxynitride film. The first layer 128 a and the secondlayer 128 b are, for example, a silicone oxide film, a siliconoxynitride film, a hafnium oxide film, a zirconium oxide film, and analuminum oxide film.

An oxygen density of the second layer 128 b is higher than an oxygendensity of the first layer 128 a. An example will be described in whichthe first layer 128 a is a silicone oxide film, and the second layer 128b is a hafnium oxide film.

The first region 129 a may be provided across the first layer 128 a andthe second layer 128 b. The first region 129 a may be provided betweenthe first layer 128 a and the second layer 128 b. The first region 129 amay be provided on an interface between the first layer 128 a and thesecond layer 128 b. The first region 129 a includes a first elementwhich is at least one element selected from the group consisting of F(fluorine), D (deuterium), and H (hydrogen).

The first region 129 a has a first concentration peak of the firstelement. A full width at half maximum of the first concentration peak isequal to or less than 1 nm. The first element segregates on theinterface between the first layer 128 a and the second layer 128 b. Aconcentration of the first element positioned 1 nm or more away from aconcentration peak of the first element is preferably sufficiently smalland equal to or less than 1×10¹⁸ cm⁻³. The element concentration can beconfirmed by a SIMS and is preferably equal to or less than a detectionlimit of each element (approximately 1×10¹⁷ cm⁻³ or less).

The second region 129 b may be provided in the first region 129 a. Thesecond region 129 b may be provided between the first region 129 a andthe first layer 128 a. The second region 129 b includes a second elementwhich is at least one element selected from the group consisting of Ge(germanium), B (boron), Al (aluminum), Ga (gallium), In (indium), Be(beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium),Sc (scandium), Y (yttrium), La (lantern), and lanthanoid (Ce, Pr, Nd,Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu).

The second region 129 b has a second concentration peak of a secondelement. A full width at half maximum of the second concentration peakis equal to or less than 1 nm. A concentration of the second elementpositioned 1 nm or more away from a concentration peak of the secondelement is preferably sufficiently small and equal to or less than1×10¹⁸ cm⁻³. The element concentration can be confirmed by a SIMS and ispreferably equal to or less than a detection limit of each element(approximately 1×10¹⁷ cm⁻³ or less). A distance of the secondconcentration peak from the first concentration peak is equal to or lessthan 4 nm. A distance of the second concentration peak from the firstconcentration peak is preferably equal to or less than 1 nm. The secondelement segregates on the first layer 128 a side of an interface betweenthe first layer 128 a and the second layer 128 b.

In the present description, a distance between peaks means a distancebetween tops of the peaks.

The second region 129 b further has a third concentration peak of C(carbon). A full width at half maximum of the third concentration peakis equal to or less than 1 nm. A concentration of C positioned 1 nm ormore away from a concentration peak of C is preferably sufficientlysmall and equal to or less than 1×10¹⁸ cm⁻³. A concentration of C can beconfirmed by a SIMS and is preferably equal to or less than a detectionlimit of C (approximately 1×10¹⁷ cm⁻³ or less). A distance of a thirdconcentration peak from the first concentration peak is equal to or lessthan 4 nm, and a distance from the second concentration peak is shorterthan the distance from the first concentration peak. The thirdconcentration peak and the second concentration peak preferably overlap.It is preferable that a top of the third concentration peak and atop ofthe second concentration peak are substantially in the same position.

Element concentrations and distribution thereof in the first layer 128a, the second layer 128 b, the first region 129 a, and the second region129 b can be calculated by, for example, a secondary ion massspectrometry (SIMS).

The MISFET 100 includes a conductive source electrode 34 electricallyconnected to the source region 18 and the p-well contact region 20. Thesource electrode 34 also functions as a p-well electrode which applies apotential to the p-well region 16.

The source electrode 34 is formed by stacking of, for example, barriermetal layers of Ni (nickel) and metal layers of Al (aluminum) on thebarrier metal layers. The barrier metal layers of Ni and the metallayers of Al may form an alloy by reaction.

Further, a conductive drain electrode 36 is formed on a side opposed tothe drift layer 14 on the SiC substrate 12, specifically on a backsurface side. The drain electrode 36 is, for example, Ni (nickel).

In the present embodiment, n-type impurity is preferably such as N(nitrogen) and P (phosphorus). However, As (arsenic) or Sb (antimony)can be applied. Further, p-type impurity is preferably such as Al(aluminum). However, such as B (boron), Ga (gallium), and In (indium)can be applied.

Functions and effects of a semiconductor device according to the presentembodiment will be described below.

In a MISFET of SiC, mobility of an electron is decreased, andon-resistance is increased due to an interface state between a SiC layerand a gate insulating layer. Therefore, for example, there is a methodin which N (nitrogen) or P (phosphorus) to terminate an interface stateare introduced into the interface between a SiC layer and an insulatinglayer. In the case where this method is used, N (nitrogen) or P(phosphorus) function as n-type dopant, and a threshold voltage may bedecreased in an n-channel type MISFET. Both a high mobility and a highthreshold voltage are required in the n-channel type MISFET.

FIG. 4 is an explanatory diagram of functions and effects according tothe present embodiment. In the present embodiment, a positive chargeexists in the first region 129 a, and a negative charge exists in thesecond region 129 b neighboring the first region 129 a. The positivecharge and the negative charge form a fixed dipole. In the fixed dipole,a gate electrode side is a positive charge, and a SiC layer 16 side is anegative charge. Therefore, a threshold voltage of an n-channel typeMISFET is increased by the fixed dipole. Accordingly, a MISFET having ahigh threshold voltage can be realized.

In the present embodiment, the gate insulating layer 128 has a stackedstructure of the first layers 128 a and the second layers 128 b whichhave different oxygen densities. Oxygen defect density is increased onan interface between the first layer 128 a and the second layer 128 bwhich have different oxygen densities. As a result of a first principlecalculation by an inventor of the present disclosure, in the case wherea first element selected from F (fluorine), D (deuterium), and H(hydrogen) is introduced into an interface with an oxygen defect, anelectron in the first element is discharged, the oxygen defect is buriedby the first element, and the first element becomes a positive fixedcharge. Accordingly, the interface is stabilized.

On the other hand, as a result of the first principle calculation by theinventor, it has been clarified that a second element selected from thegroup consisting of Ge (germanium), B (boron), Al (aluminum), Ga(gallium), In (indium), Be (beryllium), Mg (magnesium), Ca (calcium), Sr(strontium), Ba (barium), Sc (scandium), Y (yttrium), La (lantern), andlanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)is stabilized by forming a composite by combining with C (carbon) and O(oxygen) in an insulating layer, especially in a silicone oxide film. Ithas also been clarified that the composite forms an electron trap statein a silicone oxide film.

In the present embodiment, a fixed dipole is formed and stabilized whenan electron is supplied from a first element selected from F (fluorine),D (deuterium), and H (hydrogen) to a second element and a composite of C(carbon) and O (oxygen).

A first concentration peak, a second concentration peak, and a thirdconcentration peaks are preferably 1×10¹⁹ cm⁻³ or more and 4×10²² cm⁻³or less. When the concentrations are below the above range, an increaseeffect of on a threshold voltage by a fixed dipole may not be obtained.Further, it is difficult to introduce an element over the above rangeinto a film.

A second element forms a composite by combining with C (carbon) at aratio of 1:1. Therefore, an amount ratio between the second element andC (carbon) is preferably close to 1:1. Therefore, a second concentrationpeak is preferably 80% or more and 120% or less of a third concentrationpeak.

The third concentration peak and the second concentration peakpreferably overlap since a second element forms a composite by bondingwith C (carbon).

Next, a manufacturing method for a semiconductor device according to thepresent embodiment will be described with reference to FIGS. 1 and 3.Especially, a manufacturing method for the gate insulating layer 128will be described. An example will be described in which a first elementis Al (aluminum), and a second element is F (fluorine).

First, a thermal oxide film is formed on the SiC layer 16. In such acase, C (carbon) in a substrate is diffused in the thermal oxide film.This thermal oxide film becomes the first layer 128 a.

Next, a thermal nitriding process is performed in nitrogen oxideatmosphere, and a dangling bond on an interface between the SiC layer 16and a thermal oxide film is terminated by N (nitrogen).

Next, Al (aluminum) film is vapor-deposited on a thermal oxide film.Then, fluorination is performed in fluorine plasma.

Next, a hafnium oxide film is deposited by a CVD method. The hafniumoxide film becomes the second layer 128 b. Then, annealing is performedin nitrogen atmosphere. By annealing, F (fluorine) segregate to theinterface between the first layer 128 a and the second layer 128 b, andalso C (carbon) supplied from a substrate and Al supplied from an Alfilm and O (oxygen) combine, and a composite is formed. This compositeis drawn to F (fluorine) on the interface, and the first region 129 aand the second region 129 b are formed.

Then, for example, a polycrystalline gate electrode is formed.

Regarding other process steps, the MISFET 100 illustrated in FIGS. 1 and3 is formed by using a known manufacturing method.

According to the present embodiment, an n-channel type MISFET havingboth of a high mobility and a high threshold voltage can be realized.

As a method for introducing elements other than Al, as with Al, othermetal may be vapor-deposited such as Ge (germanium), B (boron), Ga(gallium), In (indium), Be (beryllium), Mg (magnesium), Ca (calcium), Sr(strontium), Ba (barium), Sc (scandium), Y (yttrium), La (lantern), andlanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu).Alternatively, the MISFET is realized by using ion implantation. If theMISFET is realized by ion implantation, carbon can be introduced in thesame region by carbon implantation. The above manufacturing methods canalso applicable to embodiments to be described below. As a method forintroducing elements other than F (fluorine), H plasma processing and Dplasma processing may be performed to introduce D (deuterium) and H(hydrogen). The above manufacturing methods can also applicable toembodiments to be described below.

Second Embodiment

In a semiconductor device according to a second embodiment, a gateinsulating layer is similar to the gate insulating layer according tothe first embodiment other than that multiple layers of the stackedstructure of first and second layers are introduced. Therefore,description of contents already described in the first embodiment willbe omitted.

FIG. 5 is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to the present embodiment. Asdescribed in FIG. 5, a gate insulating layer 128 has a two-layer stackedstructure of first layers 128 a and second layers 128 b. A first region129 a and a second region 129 b include two layers.

FIG. 6 is an explanatory diagram of functions and effects according tothe present embodiment. In the present embodiment, a two-layer fixeddipole is formed by including two layers of the stacked structure of thefirst layers 128 a and the second layers 128 b and including two layersof the first region 129 a and the second region 129 b. Increase in athreshold voltage of a MISFET is proportional to numbers of the layersof the fixed dipole. Therefore, according to the present embodiment, athreshold voltage of the MISFET is further increased in comparison withthe first embodiment.

Herein, the example has been described in which a two-layer stackedstructure of the first layers 128 a and the second layers 128 b areintroduced. However, the stacked structure can be three or more layers.Especially, a SiC-MISFET having a high breakdown voltage can have athick gate insulating layer to a certain degree. Therefore, a thresholdvoltage can be easily increased by increasing numbers of the layers.

Carbon can be sufficiently taken in the second region 129 b formed awayfrom a substrate, for example, by using a film in which TEOS is used asa precursor. Other manufacturing methods are similar to the methodsaccording to the first embodiment. In some cases, carbon may beintroduced by ion implantation. In embodiments to be described later, aSiO₂ film deposited using TEOS can be applied when carbon is needed.

Third Embodiment

In a semiconductor device according to a third embodiment, a gateinsulating layer includes a first layer, a second layer, a first region,and a second region. The second layer is provided between the firstlayer and a gate electrode and has a higher oxygen density than thefirst layer. The first region is provided in the second layer. The firstregion includes a first element which is at least one element in thegroup consisting of Ta (tantalum), Nb (niobium), and V (vanadium) andhas a first concentration peak of the first element. The second regionis provided in the first layer. The second region includes a secondelement which is at least one element selected from the group consistingof Ge (germanium), B (boron), Al (aluminum), Ga (gallium), In (indium),Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba(barium), La (lantern), and lanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, and Lu) and has a second concentration peak of thesecond element and a third concentration peak of C (carbon) in which adistance from the second concentration peak is shorter than a distancefrom the first concentration peak. The semiconductor device according tothe present embodiment is similar to the semiconductor device accordingto the first embodiment other than that a gate insulating layer has adifferent configuration. Therefore, description of contents alreadydescribed in the first embodiment will be omitted.

FIG. 7A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to the present embodiment, andFIG. 7B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode. FIG. 7A is an enlarged view ofa p-type SiC layer 16, a gate insulating layer 228, and a gate electrode30, and FIG. 7B illustrates element distribution thereof.

The gate insulating layer 228 includes a first layer 228 a, a secondlayer 228 b, a first region 229 a, and a second region 229 b. The secondlayer 228 b is provided between the first layer 228 a and the gateelectrode 30. The second layer 228 b is provided on the first layer 228a.

The first layer 228 a and the second layer 228 b are, for example, anoxide film or an oxynitride film. The first layer 228 a and the secondlayer 228 b are, for example, a silicone oxide film, a siliconoxynitride film, a hafnium oxide film, a zirconium oxide film, and analuminum oxide film.

An oxygen density in the second layer 228 b is higher than an oxygendensity in the first layer 228 a. An example will be described in whichthe first layer 228 a is a silicon oxide film, and the second layer 228b is a hafnium oxide film.

The first region 229 a may be provided in the second layer 228 b. Thefirst region 229 a may be provided between the first layer 228 a and thesecond layer 228 b. The first region 229 a may be provided on the secondlayer 228 b side on an interface between the first layer 228 a and thesecond layer 228 b. The first region 229 a includes a first elementwhich is at least one element selected from the group consisting of Ta(tantalum), Nb (niobium), and V (vanadium).

The first region has a first concentration peak of the first element. Afull width at half maximum of the first concentration peak is equal toor less than 1 nm. The first element segregates on the interface betweenthe first layer 228 a and the second layer 228 b. A concentration of thefirst element positioned 1 nm or more away from a concentration peak ofthe first element is preferably sufficiently small and equal to or lessthan 1×10¹⁸ cm⁻³. The element concentration can be confirmed by a SIMSand is preferably equal to or less than a detection limit of eachelement (approximately 1×10¹⁷ cm⁻³ or less).

The second region 229 b may be provided in the first layer 228 a. Thesecond region 229 b may be provided between the first region 229 a andthe first layer 228 a. The second region 229 b includes a second elementwhich is at least one element selected from the group consisting of Ge(germanium), B (boron), Al (aluminum), Ga (gallium), In (indium), Be(beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium),Sc (scandium), Y (yttrium), La (lantern), and lanthanoid (Ce, Pr, Nd,Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu).

The second region has a second concentration peak of the second element.A full width at half maximum of the second concentration peak is equalto or less than 1 nm. A concentration of the second element positioned 1nm or more away from a concentration peak of the second element ispreferably sufficiently small and equal to or less than 1×10¹⁸ cm⁻³. Theelement concentration can be confirmed by a SIMS and is preferably equalto or less than a detection limit of each element (approximately 1×10¹⁷cm⁻³ or less). A distance of the second concentration peak from thefirst concentration peak is equal to or less than 4 nm. A distance ofthe second concentration peak from the first concentration peak ispreferably equal to or less than 1 nm. The second element segregates onthe first layer 228 a side on the interface between the first layer 228a and the second layer 228 b.

The second region 229 b further has a third concentration peak of C(carbon). A full width at half maximum of the third concentration peakis equal to or less than 1 nm. A concentration of C positioned 1 nm ormore away from a concentration peak of C is preferably sufficientlysmall and equal to or less than 1×10¹⁸ cm⁻³. The element concentrationcan be confirmed by a SIMS and is preferably equal to or less than adetection limit of each element (approximately 1×10¹⁷ cm⁻³ or less). Adistance of a third concentration peak from the first concentration peakis equal to or less than 4 nm, and a distance from the secondconcentration peak is shorter than the distance from the firstconcentration peak. The third concentration peak and the secondconcentration peak preferably overlap. It is preferable that a top ofthe third concentration peak and a top of the second concentration peakare substantially in the same position.

Element concentrations and distribution thereof in the first layer 228a, the second layer 228 b, the first region 229 a, and the second region229 b can be calculated by, for example, a secondary ion massspectrometry (SIMS).

FIG. 8 is an explanatory diagram of functions and effects according tothe present embodiment. In the present embodiment, a positive chargeexists in the first region 229 a, and a negative charge exists in thesecond region 229 b neighboring the first region 229 a. The positivecharge and the negative charge form a fixed dipole. In the fixed dipole,a gate electrode side is a positive charge, and a SiC layer 16 side is anegative charge. Therefore, a threshold voltage of an n-channel typeMISFET is increased by the fixed dipole. Accordingly, a MISFET having ahigh threshold voltage can be realized.

In the present embodiment, a first element selected from Ta (tantalum),Nb (niobium), and V (vanadium) is fixed in the second layer 228 b havinga high oxygen density. As a result of a first principle calculation byan inventor of the present disclosure, it has been clarified that thefirst element selected from Ta (tantalum), Nb (niobium), and V(vanadium) is stabilized by replacing a metal element in the secondlayer 228 b with a high oxygen density by discharging an electron.

On the other hand, as a result of the first principle calculation by theinventor, it has been clarified that a second element selected from thegroup consisting of Ge (germanium), B (boron), Al (aluminum), Ga(gallium), In (indium), Be (beryllium), Mg (magnesium), Ca (calcium), Sr(strontium), Ba (barium), Sc (scandium), Y (yttrium), La (lantern), andlanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)is stabilized by forming a composite by combining C (carbon) and O(oxygen) in an insulating layer, especially in a silicone oxide film. Ithas also been clarified that the composite forms an electron trap statein a silicone oxide film.

In the present embodiment, a fixed dipole is formed and stabilized whenan electron is supplied from a first element selected from Ta(tantalum), Nb (niobium), and V (vanadium) to a composite of a secondelement, C (carbon) and O (oxygen).

A first concentration peak, a second concentration peak, and a thirdconcentration peak are preferably 1×10¹⁹ cm⁻³ or more and 4×10²² cm⁻³ orless. When the concentrations are below the above range, an increaseeffect on a threshold voltage by a fixed dipole may not be obtained.Further, it is difficult to introduce an element over the above rangeinto a film.

According to the present embodiment, an n-channel type MISFET havingboth of a high mobility and a high threshold voltage can be realized.

As a method for introducing elements other than Ta, as with Ta, othermetal may be vapor-deposited such as Nb (niobium) and V (vanadium).Alternatively, the MISFET is realized by using ion implantation.Further, in accordance with the second embodiment, a multi-stacked filmmay be used.

Fourth Embodiment

In a semiconductor device according to a fourth embodiment, a gateinsulating layer includes a first layer, a second layer, a first region,and a second region. The second layer is provided between the firstlayer and an gate electrode and has a lower oxygen density than thefirst layer. The first region is provided across the first layer and thesecond layer. The first region includes a first element which is atleast one element in the group consisting of N (nitrogen), P(phosphorus), As (arsenic), Sb (antimony), and Bi (bismuth) and has afirst concentration peak of the first element. The second region isprovided in the second layer. The second region includes a secondelement which is at least one element selected from the group consistingof N (nitrogen), P (phosphorus), As (arsenic), Sb (antimony), and Bi(bismuth) and has a second concentration peak of the second element anda third concentration peak of C (carbon) in which a distance from thesecond concentration peak is shorter than a distance from the firstconcentration peak.

The semiconductor device according to the present embodiment is similarto the semiconductor device according to the first embodiment other thanthat a gate insulating layer has a different configuration. Therefore,description of contents already described in the first embodiment willbe omitted.

FIG. 9A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to the present embodiment, andFIG. 9B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode. FIG. 9A is an enlarged view ofa p-type SiC layer 16, a gate insulating layer 328, and a gate electrode30, and FIG. 9B illustrates element distribution thereof.

The gate insulating layer 328 includes a first layer 328 a, a secondlayer 328 b, a first region 329 a, and a second region 329 b. The secondlayer 328 b is provided between the first layer 328 a and the gateelectrode 30. The second layer 328 b is provided on the first layer 328a.

The first layer 328 a and the second layer 328 b are, for example, anoxide film or an oxynitride film. The first layer 328 a and the secondlayer 328 b are, for example, a silicone oxide film, a siliconoxynitride film, a hafnium oxide film, a zirconium oxide film, and analuminum oxide film.

An oxygen density of the second layer 328 b is lower than an oxygendensity of the first layer 328 a. An example will be described in whichthe first layer 328 a is a hafnium oxide film, and the second layer 328b is a silicon oxide film.

The first region 329 a may be provided across the first layer 328 a andthe second layer 328 b. The first region 329 a may be provided betweenthe first layer 328 a and the second layer 328 b. The first region 329 amay be provided at an interface between the first layer 328 a and thesecond layer 328 b. The first region 329 a includes a first elementwhich is at least one element selected from the group consisting of N(nitrogen), P (phosphorus), As (arsenic), Sb (antimony), and Bi(bismuth).

The first region 329 a has a first concentration peak of the firstelement. A full width at half maximum of the first concentration peak isequal to or less than 1 nm. A concentration of the first elementpositioned 1 nm or more away from a concentration peak of the firstelement is preferably sufficiently small and equal to or less than1×10¹⁸ cm⁻³. The element concentration can be confirmed by a SIMS and ispreferably equal to or less than a detection limit of each element(approximately 1×10¹⁷ cm⁻³ or less). The first element segregates on theinterface between the first layer 328 a and the second layer 328 b.

The second region 329 b may be provided in the second layer 328 b. Thesecond region 329 b may be provided between the first region 329 a andthe second layer 328 b. The second region 329 b includes a secondelement which is at least one element selected from the group consistingof N (nitrogen), P (phosphorus), As (arsenic), Sb (antimony), and Bi(bismuth).

The second region 329 b has a second concentration peak of the secondelement. A full width at half maximum of the second concentration peakis equal to or less than 1 nm. A concentration of the second elementpositioned 1 nm or more away from a concentration peak of the secondelement is preferably sufficiently small and equal to or less than1×10¹⁸ cm⁻³. The element concentration can be confirmed by a SIMS and ispreferably equal to or less than a detection limit of each element(approximately 1×10¹⁷ cm⁻³ or less). A distance of the secondconcentration peak from the first concentration peak is equal to or lessthan 4 nm. A distance of the second concentration peak from the firstconcentration peak is preferably equal to or less than 1 nm. The secondelement segregates on the second layer 328 b side on an interfacebetween the first layer 328 a and the second layer 328 b.

The second region 329 b further has a third concentration peak of C(carbon). A full width at half maximum of the third concentration peakis equal to or less than 1 nm. A concentration of C positioned 1 nm ormore away from a concentration peak of C is preferably sufficientlysmall and equal to or less than 1×10¹⁸ cm⁻³. The element concentrationcan be confirmed by a SIMS and is preferably equal to or less than adetection limit of each element (approximately 1×10¹⁷ cm⁻³ or less). Adistance of the third concentration peak from the first concentrationpeak is equal to or less than 4 nm, and a distance from the secondconcentration peak is shorter than the distance from the firstconcentration peak. The third concentration peak and the secondconcentration peak preferably overlap. It is preferable that a top ofthe third concentration peak and a top of the second concentration peakare substantially in the same position.

Element concentrations and distribution thereof in the first layer 328a, the second layer 328 b, the first region 329 a, and the second region329 b can be calculated by, for example, a secondary ion massspectrometry (SIMS).

FIG. 10 is an explanatory diagram of functions and effects according tothe present embodiment. In the present embodiment, a negative chargeexists in the first region 329 a, and a positive charge exists in thesecond region 329 b neighboring the first region 329 a. The positivecharge and the negative charge form a fixed dipole. In the fixed dipole,a gate electrode side is a positive charge, and a SiC layer 16 side is anegative charge. Therefore, a threshold voltage of an n-channel typeMISFET is increased by the fixed dipole. Accordingly, a MISFET having ahigh threshold voltage can be realized.

In the present embodiment, the gate insulating layer 328 has a stackedstructure of the first layers 328 a and the second layers 328 b whichhave different oxygen densities. An oxygen defect density is increasedat the interface between the first layer 328 a and the second layer 328b which have different oxygen densities. As a result of a firstprinciple calculation by an inventor of the present disclosure, it hasbeen clarified that, when a first element selected from N (nitrogen), P(phosphorus), As (arsenic), Sb (antimony), and Bi (bismuth) isintroduced to the interface, the first element receives an electron, thefirst element buries an oxygen defect, and the first element becomes anegative fixed charge. Accordingly, the interface is stabilized.

On the other hand, as a result of a first principle calculation by aninventor of the present disclosure, a second element selected from thegroup consisting of N (nitrogen), P (phosphorus), As (arsenic), Sb(antimony), and Bi (bismuth) is stabilized by forming a composite bycombining with C (carbon) and O (oxygen) in an insulating layer,especially in a silicone oxide film. It has also been clarified that thecomposite discharges an electron and forms a positive charge in asilicone oxide film.

In the present embodiment, a stable fixed dipole is formed by supply ofan electron from the composite of a second element, C (carbon) and O(oxygen) to a first element selected from N (nitrogen), P (phosphorus),As (arsenic), Sb (antimony), and Bi (bismuth).

A first concentration peak, a second concentration peak, and a thirdconcentration peak are preferably 1×10¹⁹ cm⁻³ or more and 4×10²² cm⁻³ orless. When the concentrations are below the above range, an increaseeffect on a threshold voltage by a fixed dipole may not be obtained.Further, it is difficult to introduce an element over the above rangeinto a film.

According to the present embodiment, an n-channel type MISFET havingboth of a high mobility and a high threshold voltage can be realized.

As a method for introducing N (nitrogen), P (phosphorus), As (arsenic),Sb (antimony), and Bi (bismuth), plasma processing may be performed ineach element after an HfO₂ film is formed. Then, SiO₂, in which TEOS isused as a precursor, is formed thereon. Thus, a stacked film accordingto the embodiment is formed. Herein, instead of the plasma processing,elements such as N, P, As, Sb, and Bi may be adsorbed by performing NH₃,PH₃, AsH₃, SbH₃, and BiH₃ processing. Further, in accordance with thesecond embodiment, a multi-stacked film may be used.

Fifth Embodiment

In a semiconductor device according to a fifth embodiment, a gateinsulating layer includes a first layer, a second layer, a first region,and a second region. The second layer is provided between the firstlayer and the gate electrode and has a higher oxygen density than thefirst layer. The first region is provided in the first layer. The firstregion includes a first element which is at least one element in thegroup consisting of Mg (magnesium), Ca (calcium), Sr (strontium), Ba(barium), Sc (scandium), Y (yttrium), La (lantern), and lanthanoid (Ce,Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) and has a firstconcentration peak of the first element. The second region is providedin the second layer. The second region includes a second element whichis at least one element in the group consisting of N (nitrogen), P(phosphorus), As (arsenic), Sb (antimony), and Bi (bismuth) and has asecond concentration peak of the second element and a thirdconcentration peak of C (carbon) in which a distance from the secondconcentration peak is shorter than a distance from the firstconcentration peak.

The semiconductor device according to the present embodiment is similarto the semiconductor device according to the first embodiment other thanthat a gate insulating layer has a different configuration. Therefore,description of contents already described in the first embodiment willbe omitted.

FIG. 11A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to the present embodiment, andFIG. 11B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode. FIG. 11A is an enlarged viewof a p-type SiC layer 16, a gate insulating layer 428, and a gateelectrode 30, and FIG. 11B illustrates element distribution thereof.

A gate insulating layer 428 includes a first layer 428 a, a second layer428 b, a first region 429 a, and a second region 429 b. The second layer428 b is provided between the first layer 428 a and the gate electrode30. The second layer 428 b is provided on the first layer 428 a.

The first layer 428 a and the second layer 428 b are, for example, anoxide film or an oxynitride film. The first layer 428 a and the secondlayer 428 b are, for example, a silicone oxide film, a siliconoxynitride film, a hafnium oxide film, a zirconium oxide film, and analuminum oxide film.

An oxygen density of the second layer 428 b is lower than an oxygendensity of the first layer 428 a. An example will be described in whichthe first layer 428 a is a hafnium oxide film, and the second layer 428b is a silicon oxide film.

The first region 429 a may be provided in the first layer 428 a. Thefirst region 429 a may be provided between the first layer 428 a and thesecond layer 428 b. The first region 429 a may be provided on the firstlayer 428 a side on an interface between the first layer 428 a and thesecond layer 428 b. The first region 429 a includes a first elementwhich is at least one element selected from the group consisting of Mg(magnesium), Ca (calcium), Sr (strontium), Ba (barium), Sc (scandium), Y(yttrium), La (lantern), and lanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, and Lu).

The first region 429 a has a first concentration peak of the firstelement. A full width at half maximum of the first concentration peak isequal to or less than 1 nm. The first element segregates on the firstlayer 428 a side on an interface between the first layer 428 a and thesecond layer 428 b. A concentration of the first element positioned 1 nmor more away from a concentration peak of the first element ispreferably sufficiently small and equal to or less than 1×10¹⁸ cm⁻³. Theelement concentration can be confirmed by a SIMS and is preferably equalto or less than a detection limit of each element (approximately 1×10¹⁷cm⁻³ or less).

The second region 429 b may be provided in the second layer 428 b. Thesecond region 429 b may be provided between the first region 429 a andthe second layer 428 b. The second region 429 b includes a secondelement which is at least one element selected from the group consistingof N (nitrogen), P (phosphorus), As (arsenic), Sb (antimony), and Bi(bismuth).

The second region 429 b has a second concentration peak of the secondelement. A full width at half maximum of the second concentration peakis equal to or less than 1 nm. A concentration of the second elementpositioned 1 nm or more away from a concentration peak of the secondelement is preferably sufficiently small and equal to or less than1×10¹⁸ cm⁻³. The element concentration can be confirmed by a SIMS and ispreferably equal to or less than a detection limit of each element(approximately 1×10¹⁷ cm⁻³ or less). A distance of the secondconcentration peak from the first concentration peak is equal to or lessthan 4 nm. A distance of the second concentration peak from the firstconcentration peak is preferably equal to or less than 1 nm. The secondelement segregates at the second layer 428 b side on an interfacebetween the first layer 428 a and the second layer 428 b.

The second region 429 b further has a third concentration peak of C(carbon). A full width at half maximum of the third concentration peakis equal to or less than 1 nm. A concentration of C positioned 1 nm ormore away from a concentration peak of C is preferably sufficientlysmall and equal to or less than 1×10¹⁸ cm⁻³. The element concentrationcan be confirmed by a SIMS and is preferably equal to or less than adetection limit of each element (approximately 1×10¹⁷ cm⁻³ or less). Adistance of a third concentration peak from the first concentration peakis equal to or less than 4 nm, and a distance from the secondconcentration peak is shorter than the distance from the firstconcentration peak. The third concentration peak and the secondconcentration peak preferably overlap. It is preferable that a top ofthe third concentration peak and a top of the second concentration peakare substantially in the same position.

Element concentrations and distribution thereof in the first layer 428a, the second layer 428 b, the first region 429 a, and the second region429 b can be calculated by, for example, a secondary ion massspectrometry (SIMS).

FIG. 12 is an explanatory diagram of functions and effects according tothe present embodiment. In the present embodiment, a negative chargeexists in the first region 429 a, and a positive charge exists in thesecond region 429 b neighboring the first region 429 a. The positivecharge and the negative charge form a fixed dipole. In the fixed dipole,a gate electrode side is a positive charge, and a SiC layer 16 side is anegative charge. Therefore, a threshold voltage of an n-channel typeMISFET is increased by the fixed dipole. Accordingly, a MISFET having ahigh threshold voltage can be realized.

In the present embodiment, a first element selected from Mg (magnesium),Ca (calcium), Sr (strontium), Ba (barium), Sc (scandium), Y (yttrium),La (lantern), and lanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb, and Lu) is fixed in the second layer 328 b having a highoxygen density, and forms a negative charge.

On the other hand, as a result of a first principle calculation by aninventor of the present disclosure, a second element selected from thegroup consisting of N (nitrogen), P (phosphorus), As (arsenic), Sb(antimony), and Bi (bismuth) is stabilized by forming a composite bycombining with C (carbon) and O (oxygen) in an insulating layer,especially in a silicone oxide film. It has also been clarified that apositive charge is formed by discharging an electron in a silicone oxidefilm.

In the present embodiment, a fixed dipole is formed in which a negativecharge of a first element selected from Mg (magnesium), Ca (calcium), Sr(strontium), Ba (barium), Sc (scandium), Y (yttrium), La (lantern), andlanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)and positive charges of the composite of a second element, C (carbon)and O (oxygen) are stabilized.

A first concentration peak, a second concentration peak, and a thirdconcentration peak are preferably 1×10¹⁹ cm⁻³ or more and 4×10²² cm⁻³ orless. When the concentrations are below the above range, an increaseeffect on a threshold voltage by a fixed dipole may not be obtained.Further, it is difficult to introduce an element over the above rangeinto a film.

According to the present embodiment, an n-channel type MISFET havingboth of a high mobility and a high threshold voltage can be realized.

As a method for introducing Mg (magnesium), Ca (calcium), Sr(strontium), Ba (barium), Sc (scandium), Y (yttrium), La (lantern), andlanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu),metal of each element may be vapor-deposited after an HfO₂ film isformed. Then, plasma processing is performed in N (nitrogen), P(phosphorus), As (arsenic), Sb (antimony), and Bi (bismuth), and SiO₂ inwhich TEOS is used as a precursor is formed. Thus, a stacked filmaccording to the embodiment is formed. Herein, instead of the plasmaprocessing, elements such as N, P, As, Sb, and Bi may be adsorbed byperforming NH₃, PH₃, AsH₃, SbH₃, and BiH₃ processing. Further, inaccordance with the second embodiment, a multi-stacked film may be used.

Sixth Embodiment

In a semiconductor device according to a sixth embodiment, a gateinsulating layer includes a first layer, a second layer, a first region,and a second region. The second layer is provided between the firstlayer and a gate electrode and has a higher oxygen density than thefirst layer. The first region is provided across the first layer and thesecond layer. The first region includes a first element which is atleast one element in the group consisting of N (nitrogen), P(phosphorus), As (arsenic), Sb (antimony), and Bi (bismuth) and has afirst concentration peak of the first element. The second region isprovided in the second layer. The second region includes a secondelement which is at least one element in the group consisting of Ta(tantalum), Nb (niobium), and V (vanadium) and has a secondconcentration peak of the second element. The semiconductor deviceaccording to the present embodiment is similar to the semiconductordevice according to the first embodiment other than that a gateinsulating layer has a different configuration. Therefore, descriptionof contents already described in the first embodiment will be omitted.

FIG. 13A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to the present embodiment, andFIG. 13B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode. FIG. 13A is an enlarged viewof a p-type SiC layer 16, a gate insulating layer 528, and a gateelectrode 30, and FIG. 13B illustrates element distribution thereof.

A gate insulating layer 528 includes a first layer 528 a, a second layer528 b, a first region 529 a, and a second region 529 b. The second layer528 b is provided between the first layer 528 a and the gate electrode30. The second layer 528 b is provided on the first layer 528 a.

The first layer 528 a and the second layer 528 b are, for example, anoxide film or an oxynitride film. The first layer 528 a and the secondlayer 528 b are, for example, a silicone oxide film, a siliconoxynitride film, a hafnium oxide film, a zirconium oxide film, and analuminum oxide film.

An oxygen density in the second layer 528 b is higher than an oxygendensity in the first layer 528 a. An example will be described in whichthe first layer 528 a is a silicon oxide film, and the second layer 528b is a hafnium oxide film.

The first region 529 a may be provided across the first layer 528 a andthe second layer 528 b. The first region 529 a may be provided betweenthe first layer 528 a and the second layer 528 b. The first region 529 amay be provided at an interface between the first layer 528 a and thesecond layer 528 b. The first region 529 a includes a first elementwhich is at least one element selected from the group consisting of N(nitrogen), P (phosphorus), As (arsenic), Sb (antimony), and Bi(bismuth).

The first region 529 a has a first concentration peak of the firstelement. A full width at half maximum of the first concentration peak isequal to or less than 1 nm. The first element segregates at theinterface between the first layer 528 a and the second layer 528 b. Aconcentration of the first element positioned 1 nm or more away from aconcentration peak of the first element is preferably sufficiently smalland equal to or less than 1×10¹⁸ cm⁻³. The element concentration can beconfirmed by a SIMS and is preferably equal to or less than a detectionlimit of each element (approximately 1×10¹⁷ cm⁻³ or less).

The second region 529 b may be provided in the second layer 528 b. Thesecond region 529 b may be provided between the first region 529 a andthe second layer 528 b. The second region 529 b includes a secondelement which is at least one element selected from the group consistingof Ta (tantalum), Nb (niobium), and V (vanadium).

The second region 529 b has a second concentration peak of the secondelement. A full width at half maximum of the second concentration peakis equal to or less than 1 nm. A concentration of the second elementpositioned 1 nm or more away from a concentration peak of the secondelement is preferably sufficiently small and equal to or less than1×10¹⁸ cm⁻³. The element concentration can be confirmed by a SIMS and ispreferably equal to or less than a detection limit of each element(approximately 1×10¹⁷ cm⁻³ or less). A distance of the secondconcentration peak from the first concentration peak is equal to or lessthan 4 nm. A distance of the second concentration peak from the firstconcentration peak is preferably equal to or less than 1 nm. The secondelement segregates on the second layer 528 b side on an interfacebetween the first layer 528 a and the second layer 528 b.

The second region 529 b preferably further has a third concentrationpeak of C (carbon). A full width at half maximum of the thirdconcentration peak is equal to or less than 1 nm. A concentration of Cpositioned 1 nm or more away from a concentration peak of C ispreferably sufficiently small and equal to or less than 1×10¹⁸ cm⁻³. Theelement concentration can be confirmed by a SIMS and is preferably equalto or less than a detection limit of each element (approximately 1×10¹⁷cm⁻³ or less). A distance of a third concentration peak from the firstconcentration peak is equal to or less than 4 nm, and a distance fromthe second concentration peak is shorter than the distance from thefirst concentration peak. The third concentration peak and the secondconcentration peak preferably overlap. It is preferable that a top ofthe third concentration peak and a top of the second concentration peakare substantially in the same position.

Element concentrations and distribution thereof in the first layer 528a, the second layer 528 b, the first region 529 a, and the second region529 b can be calculated by, for example, a secondary ion massspectrometry (SIMS).

FIG. 14 is an explanatory diagram of functions and effects according tothe present embodiment. In the present embodiment, a negative chargeexists in the first region 529 a, and a positive charge exists in thesecond region 529 b neighboring the first region 529 a. The positivecharge and the negative charge form a fixed dipole. In the fixed dipole,a gate electrode side is a positive charge, and a SiC layer 16 side is anegative charge. Therefore, a threshold voltage of an n-channel typeMISFET is increased by the fixed dipole. Accordingly, a MISFET having ahigh threshold voltage can be realized.

In the present embodiment, the gate insulating layer 528 has a stackedstructure of the first layers 528 a and the second layers 528 b whichhave different oxygen densities. An oxygen defect density is increasedon the interface between the first layer 528 a and the second layer 528b which have different oxygen densities. As a result of a firstprinciple calculation by an inventor of the present disclosure, it hasbeen clarified that, when a first element selected from N (nitrogen), P(phosphorus), As (arsenic), Sb (antimony), and Bi (bismuth) isintroduced to the interface, the first element receives an electron, thefirst element buries an oxygen defect, and the first element becomes anegative fixed charge. Accordingly the first element is stabilized.

In the present embodiment, a second element selected from Ta (tantalum),Nb (niobium), and V (vanadium) is fixed in the second layer 528 b whichhas a high oxygen density, and a positive electrical charge is formed.The second element is stabilized by coexisting with C (carbon).

Therefore, in the present embodiment, an electron is supplied from asecond element selected from Ta (tantalum), Nb (niobium), and V(vanadium) to a first element selected from N (nitrogen), P(phosphorus), As (arsenic), Sb (antimony), and Bi (bismuth) on aninterface. Accordingly, a fixed dipole is formed, and the interface isstabilized.

A first concentration peak, a second concentration peak, and a thirdconcentration peak are preferably 1×10¹⁹ cm⁻³ or more and 4×10²² cm⁻³ orless. When the concentrations are below the above range, an increaseeffect on a threshold voltage by a fixed dipole may not be obtained.Further, it is difficult to introduce an element over the above rangeinto a film.

According to the present embodiment, an n-channel type MISFET havingboth of a high mobility and a high threshold voltage can be realized.

A method for introducing each element may be followed to the embodimentsdescribed above. In accordance with the second embodiment, amulti-staked film may be used.

In the case where C is introduced into HfO₂, a CVD film in which aprecursor including C is used may be formed. Further C may be introducedby ion plantation. Alternatively, C diffused from a substrate can beused if the substrate is oxidized.

Seventh Embodiment

In a semiconductor device according to a seventh embodiment, a gateinsulating layer includes a first layer, a second layer, a first region,and a second region. The second layer is provided between the firstlayer and a gate electrode and has a lower oxygen density than the firstlayer. The first region is provided across the first layer and thesecond layer. The first region includes a first element which is atleast one element in the group consisting of F (fluorine), D(deuterium), and H (hydrogen) and has a first concentration peak of thefirst element. The second region is provided in the first layer. Thesecond region includes a second element which is at least one element inthe group consisting of Mg (magnesium), Ca (calcium), Sr (strontium), Ba(barium), Sc (scandium), Y (yttrium), La (lantern), and lanthanoid (Ce,Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), and has asecond concentration peak of the second element.

The semiconductor device according to the present embodiment is similarto the semiconductor device according to the first embodiment other thanthat a gate insulating layer has a different configuration. Therefore,description of contents already described in the first embodiment willbe omitted.

FIG. 15A is an enlarged view of a p-type SiC layer, a gate insulatinglayer, and a gate electrode according to the present embodiment, andFIG. 15B illustrates element distribution of the SiC layer, the gateinsulating layer, and the gate electrode. FIG. 15A is an enlarged viewof a p-type SiC layer 16, a gate insulating layer 628, and a gateelectrode 30, and FIG. 15B illustrates element distribution thereof.

A gate insulating layer 628 includes a first layer 628 a, a second layer628 b, a first region 629 a, and a second region 629 b. The second layer628 b is provided between the first layer 628 a and the gate electrode30. The second layer 628 b is provided on the first layer 628 a.

The first layer 628 a and the second layer 628 b are, for example, anoxide film or an oxynitride film. The first layer 628 a and the secondlayer 628 b are, for example, a silicone oxide film, a siliconoxynitride film, a hafnium oxide film, a zirconium oxide film, and analuminum oxide film.

An oxygen density of the second layer 628 b is lower than an oxygendensity of the first layer 628 a. An example will be described in whichthe first layer 628 a is a hafnium oxide film, and the second layer 628b is a silicone oxide film.

The first region 629 a may be provided between the first layer 628 a andthe second layer 628 b. The first region 629 a may be provided betweenthe first layer 628 a and the second layer 628 b. The first region 629 amay be provided at an interface between the first layer 628 a and thesecond layer 628 b. The first region 629 a includes a first elementwhich is at least one element selected from the group consisting of F(fluorine), D (deuterium), and H (hydrogen).

The first region 629 a has a first concentration peak of the firstelement. A full width at half maximum of the first concentration peak isequal to or less than 1 nm. The first element segregates on theinterface between the first layer 628 a and the second layer 628 b. Aconcentration of the first element positioned 1 nm or more away from aconcentration peak of the first element is preferably sufficiently smalland equal to or less than 1×10¹⁸ cm⁻³. The element concentration can beconfirmed by a SIMS and is preferably equal to or less than a detectionlimit of each element (approximately 1×10¹⁷ cm⁻³ or less).

The second region 629 b may be provided in the first layer 628 a. Thesecond region 629 b may be provided between the first region 629 a andthe first layer 628 a. The second region 629 b includes a second elementwhich is at least one element selected from the group consisting of Mg(magnesium), Ca (calcium), Sr (strontium), Ba (barium), Sc (scandium), Y(yttrium), La (lantern), and lanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, and Lu).

The second region 629 b has a second concentration peak of the secondelement. A full width at half maximum of the second concentration peakis equal to or less than 1 nm. A concentration of the second elementpositioned 1 nm or more away from a concentration peak of the secondelement is preferably sufficiently small and equal to or less than1×10¹⁸ cm⁻³. The element concentration can be confirmed by a SIMS and ispreferably equal to or less than a detection limit of each element(approximately 1×10¹⁷ cm⁻³ or less). A distance of the secondconcentration peak from the first concentration peak is equal to or lessthan 4 nm. A distance of the second concentration peak from the firstconcentration peak is preferably equal to or less than 1 nm. The secondelement segregates on the first layer 628 a side on an interface betweenthe first layer 628 a and the second layer 628 b.

The second region 629 b preferably further has a third concentrationpeak of C (carbon). A full width at half maximum of the thirdconcentration peak is equal to or less than 1 nm. A concentration of Cpositioned 1 nm or more away from a concentration peak of C ispreferably sufficiently small and equal to or less than 1×10¹⁸ cm⁻³. Theelement concentration can be confirmed by a SIMS and is preferably equalto or less than a detection limit of each element (approximately 1×10¹⁷cm⁻³ or less). A distance of a third concentration peak from the firstconcentration peak is equal to or less than 4 nm, and a distance fromthe second concentration peak is shorter than the distance from thefirst concentration peak. The third concentration peak and the secondconcentration peak preferably overlap. It is preferable that a top ofthe third concentration peak and a top of the second concentration peakare substantially in the same position.

Element concentrations and distribution thereof in the first layer 628a, the second layer 628 b, the first region 629 a, and the second region629 b can be calculated by, for example, a secondary ion massspectrometry (SIMS).

FIG. 16 is an explanatory diagram of functions and effects according tothe present embodiment. In the present embodiment, a positive chargeexists in the first region 629 a, and a negative charge exists in thesecond region 629 b neighboring the first region 629 a. The positivecharge and the negative charge form a fixed dipole. In the fixed dipole,a gate electrode side is a positive charge, and a SiC layer 16 side is anegative charge. Therefore, a threshold voltage of an n-channel typeMISFET is increased by the fixed dipole. Accordingly, a MISFET having ahigh threshold voltage can be realized.

In the present embodiment, the gate insulating layer 628 has a stackedstructure of the first layers 628 a and the second layers 628 b whichhave different oxygen densities. An oxygen defect density is increasedon the interface between the first layer 628 a and the second layer 628b which have different oxygen densities. As a result of a firstprinciple calculation by an inventor of the present disclosure, in thecase where a first element selected from F (fluorine), D (deuterium),and H (hydrogen) is introduced to an interface with an oxygen defect,the first element discharge an electron, the first element burries theoxygen defect, and the first element become a positive fixed charge.Accordingly, the first element is stabilized.

In the present embodiment, a second element selected from Mg(magnesium), Ca (calcium), Sr (strontium), Ba (barium), Sc (scandium), Y(yttrium), La (lantern), and lanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, and Lu) is fixed in the first layer 628 a having ahigh oxygen density. The second element is stabilized by coexisting withC (carbon).

Therefore, in the present embodiment, a fixed dipole is formed andstabilized since an electron is supplied from a first element selectedfrom F (fluorine), D (deuterium), and H (hydrogen) on an interface to asecond element selected from Mg (magnesium), Ca (calcium), Sr(strontium), Ba (barium), Sc (scandium), Y (yttrium), La (lantern), andlanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)in the first layer 628 a having a high oxygen density.

A first concentration peak, a second concentration peak, and a thirdconcentration peak are preferably 1×10¹⁹ cm⁻³ or more and 4×10²² cm⁻³ orless. When the concentrations are below the above range, an increaseeffect on a threshold voltage by a fixed dipole may not be obtained.Further, it is difficult to introduce an element over the above rangeinto a film.

According to the present embodiment, an n-channel type MISFET havingboth of a high mobility and a high threshold voltage can be realized.

A method for introducing each element may be followed to the embodimentsdescribed above. In accordance with the second embodiment, amulti-staked film may be used.

Eighth Embodiment

An inverter circuit and a driving device according to an eighthembodiment are a driving device including the semiconductor deviceaccording to the first embodiment.

FIG. 17 is a schematic view of the driving device according to thepresent embodiment. A driving device 1100 includes a motor 140 and aninverter circuit 150.

The inverter circuit 150 includes three semiconductor modules 100 a, 100b, and 100 c in which the MISFET 100 according to the first embodimentis a switching element. The three semiconductor modules 100 a, 100 b,and 100 c are connected in parallel. Accordingly, the three-phaseinverter circuit 150 including three AC voltage output terminals U, V,and W is realized. The motor 140 is driven by an AC voltage output fromthe inverter circuit 150.

According to the present embodiment, operation of the inverter circuit150 and the driving device 1100 are stabilized by providing a MISFEThaving a high threshold voltage.

Ninth Embodiment

A vehicle according to a ninth embodiment is a vehicle including thesemiconductor device according to the first embodiment.

FIG. 18 is a schematic view of the vehicle according to the presentembodiment. A vehicle 1200 according to the present embodiment is arailroad vehicle. The vehicle 1200 includes a motor 140 and an invertercircuit 150.

The inverter circuit 150 includes three semiconductor modules 100 a, 100b, and 100 c in which the MISFET 100 according to the first embodimentis a switching element. The three semiconductor modules 100 a, 100 b,and 100 c are connected in parallel. Accordingly, the three-phaseinverter circuit 150 including three AC voltage output terminals U, V,and W is realized.

The motor 140 is driven by an AC voltage output from the invertercircuit 150. A wheel 90 of the vehicle 1200 is rotated by the motor 140.

According to the present embodiment, operability of the vehicle 1200 isstabilized by including a MISFET having a high threshold voltage.

Tenth Embodiment

A vehicle according to a tenth embodiment is a vehicle including thesemiconductor device according to the first embodiment.

FIG. 19 is a schematic view of the vehicle according to the presentembodiment. A vehicle 1300 according to the present embodiment is anautomobile. The vehicle 1300 includes a motor 140 and an invertercircuit 150.

The inverter circuit 150 includes three semiconductor modules 100 a, 100b, and 100 c in which the MISFET 100 according to the first embodimentis a switching element. The three semiconductor modules 100 a, 100 b,and 100 c are connected in parallel. Accordingly, the three-phaseinverter circuit 150 including three AC voltage output terminals U, V,and W is realized.

The motor 140 is driven by an AC voltage output from the invertercircuit 150. A wheel 90 of the vehicle 1300 is rotated by the motor 140.

According to the present embodiment, reliability of the vehicle 1300 isimproved by including a MISFET having a high threshold voltage.

Eleventh Embodiment

An elevator according to an eleventh embodiment is an elevator includingthe semiconductor device according to the first embodiment.

FIG. 20 is a schematic view of an elevator according to the presentembodiment. An elevator 1400 according to the present embodimentincludes an elevator car 1010, a counterweight 1012, a wire rope 1014, ahoisting machine 1016, a motor 140, and an inverter circuit 150.

The inverter circuit 150 includes three semiconductor modules 100 a, 100b, and 100 c in which the MISFET 100 according to the first embodimentis a switching element. The three semiconductor modules 100 a, 100 b,and 100 c are connected in parallel. Accordingly, the three-phaseinverter circuit 150 including three AC voltage output terminals U, V,and W is realized.

The motor 140 is driven by an AC voltage output from the invertercircuit 150. By the motor 140, the hoisting machine 1016 rotates, andthe elevator car 1010 moves up and down.

According to the present embodiment, reliability of the elevator 1400 isimproved by including a MISFET having a high threshold voltage.

In the first to seventh embodiments, an example in which a crystalstructure of silicon carbide is 4H—SiC has been described above.However, the present disclosure can be applied to silicon carbide withother crystal structures such as 6H—SiC and 3C—SiC.

Further, in the first to seventh embodiments, the example has beendescribed in which a MISFET is an n-channel type and a planer type.However, the present disclosure can be applied to an n-channel type anda trench type MISFET. Furthermore, the present disclosure can be appliedto an n-channel type insulated gate bipolar transistor (IGBT).

In the third to seventh embodiments, a gate insulating layer can includemultiple stacked structures of first layers and second layers and caninclude a multilayer fixed dipole.

Further, a gate insulating layer in which layer configurations invarious embodiments are combined can be provided to a semiconductordevice. For example, by combining the first embodiment and the seventhembodiment, an interface of a stacked film can be effectively used.

Although a conventional charge trapping film needs charge injection, anelectrical charge can be injected in high density. However, theconventional charge trapping film has a problem that a threshold voltageis lowered since an electrical charge is discharged with a lapse oftime. This means a trapping state is not very stable.

On the other hand, in the above embodiments, stable dipole can be formedin a gate insulating layer. The dipole is very stable. Therefore, anelectrical charge does not released or introduced from the insulatinglayer. One concern may be a shift amount of threshold voltage cannot beincreased since a trap amount cannot be increased much. However, theshift amount can be increased by using a multi-stacked film. The shiftamount per dipole can be 1 to 5 V. Therefore, the targeted 5V may beachieved by stacking 1 to 3 dipoles. Further, when the shift amount isincreased to 7 V which is higher than 5 V, the dipole is furtherstabilized, and it is very effective. When the interface between a SiClayer and an insulating layer is certainly terminated, mobility isincreased, but a threshold voltage is decreased. In the embodimentsdescribed above, a threshold voltage can be freely controlled by astacked structure of a gate insulating layer independent of termination.

Further, in the ninth to eleventh embodiments, an example has beendescribed in which the semiconductor device according to the presentdisclosure is applied to a vehicle and an elevator. However, thesemiconductor device according to the present disclosure can be appliedto, for example, a power conditioner in a solar power generation system.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the semiconductor device, the invertercircuit, the driving device, the vehicle, and the elevator describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the devices andmethods described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

What is claimed is:
 1. A semiconductor device, comprising: a p-type SiClayer; a gate electrode; and a gate insulating layer provided betweenthe SiC layer and the gate electrode, the gate insulating layerincluding: a first layer, a second layer provided between the firstlayer and the gate electrode, the second layer having a higher oxygendensity than the first layer, a first region provided in the secondlayer, the first region including a first element which is at least oneelement in the group of Ta (tantalum), Nb (niobium), and V (vanadium)and the first region having a first concentration peak of the firstelement; and a second region provided in the first layer, the secondregion including a second element which is at least one element in thegroup of Ge (germanium), B (boron), Al (aluminum), Ga (gallium), In(indium), Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium),Ba (barium), La (lantern), and lanthanoid (Ce, Pr, Nd, Pm, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, and Lu) and the second region having a secondconcentration peak of the second element and a third concentration peakof C (carbon), a distance between the second concentration peak and thethird concentration peak being shorter than a distance between the firstconcentration peak and the third concentration peak.
 2. Thesemiconductor device according to claim 1, wherein a distance betweenthe second concentration peak and the first concentration peak is equalto or less than 4 nm, and the distance between the first concentrationpeak and the third concentration peak is equal to or less than 4 nm. 3.The semiconductor device according to claim 1, wherein full widths athalf maximum of the first concentration peak and the secondconcentration peak are equal to or less than 1 nm.
 4. The semiconductordevice according to claim 1, wherein a full width at half maximum of thethird concentration peak is equal to or less than 1 nm.
 5. Thesemiconductor device according to claim 1, wherein the first layer is asilicone oxide film.
 6. The semiconductor device according to claim 1,wherein the second layer is a hafnium oxide film or a zirconium oxidefilm.
 7. A semiconductor device, comprising: a p-type SiC layer; a gateelectrode; and a gate insulating layer provided between the SiC layerand the gate electrode, the gate insulating layer including: a firstlayer, a second layer provided between the first layer and the gateelectrode, the second layer having a lower oxygen density than the firstlayer, a first region provided across the first layer and the secondlayer, the first region including a first element which is at least oneelement in the group of N (nitrogen), P (phosphorus), As (arsenic), Sb(antimony), and Bi (bismuth) and the first region having a firstconcentration peak of the first element, and a second region provided inthe second layer, the second region including a second element which isat least one element in the group of N (nitrogen), P (phosphorus), As(arsenic), Sb (antimony), and Bi (bismuth) and the second region havinga second concentration peak of the second element and a thirdconcentration peak of C (carbon), a distance between the secondconcentration peak and the third concentration peak being shorter than adistance between the first concentration peak and the thirdconcentration peak.
 8. The semiconductor device according to claim 7,wherein a distance between the second concentration peak and the firstconcentration peak is equal to or less than 4 nm, and the distancebetween the first concentration peak and the third concentration peak isequal to or less than 4 nm.
 9. The semiconductor device according toclaim 7, wherein full widths at half maximum of the first concentrationpeak and the second concentration peak are equal to or less than 1 nm.10. The semiconductor device according to claim 7, wherein a full widthat half maximum of the third concentration peak is equal to or less than1 nm.
 11. The semiconductor device according to claim 7, wherein thesecond layer is a silicone oxide film.
 12. The semiconductor deviceaccording to claim 7, wherein the first layer is a hafnium oxide film ora zirconium oxide film.
 13. An inverter circuit, comprising thesemiconductor device according to claim
 1. 14. A vehicle comprising thesemiconductor device according to claim
 1. 15. An inverter circuit,comprising the semiconductor device according to claim
 7. 16. A vehiclecomprising the semiconductor device according to claim 7.